1. Field of the Invention
The present invention relates to microwave couplers in rf waveguide and particularly to hydrid couplers providing a shift from linear to circular polarization.
2. Description of the Prior Art
Generally this type of coupler has been known for a considerable length of time. It is believed the earliest knowledge of it extends at least back to the nineteen fifties. The most recent work and probably the closest to the applicant's invention is described in the article: "A WIDE-BAND SQUARE-WAVEGUIDE ARRAY POLARIZER", by Ming Hui Chen and G. N. Tsandoulas, published in the IEEE Transactions on Antennas and Propagation, May, 1973, pages 389 through 391. Other publications relating to this type of polarizer are cited in the above article.
The Chen and Tsandoulas coupler utilizes a stepped septum. The stepped septum is alleged to provide better isolation over a wider bandwidth than can be obtained with a sloped septum. In accordance with the article, the stepped septum, in achieving maximum isolation, loses some phase orthogonality. This requires correction with a dielectric slab.
The article describing the Chen and Tsandoulas coupler indicates that 20 db isolation over a 10 per cent frequency band is typical for a sloping septum and that their stepped septum provides 26 db over a 20 per cent band.